System for operating an internal combustion engine with direct injection, specially in a motor vehicle

ABSTRACT

An internal combustion engine for a motor vehicle is described which is provided with an injection valve with which fuel can be injected directly into the combustion chamber either in a first mode of operation during a compression phase or in a second mode of operation during an induction phase. Furthermore, the engine is provided with means for feeding back the exhaust gas into the combustion chamber as well as with a control apparatus for controlling (open loop and/or closed loop) the quantity of the fed back exhaust gas. According to the invention, the quantity of the exhaust gas, which is fed back into the combustion chamber, can be controlled (open loop and/or closed loop) differently in the two modes of operation.

FIELD OF THE INVENTION

The invention relates to a method for operating an internal combustionengine of a motor vehicle wherein the fuel is injected directly into thecombustion chamber of the engine either in a first operating mode duringa compression phase or in a second operating mode during an intake phaseand the fuel is combusted in the combustion chamber. In the method, atleast a portion of the exhaust gas, which is generated in thecombustion, is fed back into the combustion chamber. Furthermore, theinvention relates to an internal combustion engine especially for amotor vehicle. The engine has an injection valve with which fuel can beinjected directly into a combustion chamber either in a first mode ofoperation during a combustion phase or in a second mode of operationduring an intake phase. The engine also includes means for feeding backthe exhaust gas into the combustion chamber and has a control apparatusfor controlling (open loop/closed loop) the quantity of exhaust gas fedback.

BACKGROUND OF THE INVENTION

A system of this kind for operating an internal combustion engine havingdirect injection especially for a motor vehicle is generally known andis continuously further developed with respect to a further reduction offuel and a reduction of exhaust gas.

In this connection, a so-called stratified charge operation as a firstoperating mode and a so-called homogeneous operation as a secondoperating mode are distinguished. The stratified charge operation isespecially used for small loads; whereas, the homogeneous operation isapplied for larger loads applied to the engine. In the stratified chargeoperation, the fuel is injected into the combustion chamber during thecombustion phase and is there injected in the immediate vicinity of aspark plug. The fuel can however also be injected further distant fromthe spark plug and can be conducted to the spark plug via a movement ofair. This has the consequence that no uniform distribution of the fuelcan take place in the combustion chamber. The advantage of thestratified operation is that the applied smaller loads can be handled bythe engine with a very small quantity of fuel. Larger loads, however,cannot be satisfied in the stratified charge operation. In thehomogeneous operation, which is provided for such larger loads, the fuelis injected during the intake phase of the engine so that a swirling andtherefore a distribution of the fuel in the combustion chamber can stilleasily take place. To this extent, the homogeneous operation correspondsapproximately to the operation of internal combustion engines whereinfuel is injected into the intake manifold in the conventional manner.

In both modes of operation, that is, in the stratified load operationand in the homogeneous operation, the fuel quantity to be injected iscontrolled (open loop and/or closed loop) to an optimal value independence upon a plurality of input quantities with respect to areduction of fuel, a reduction of exhaust gas and the like.

Here it is advantageous for the reduction of the generated exhaust gaswhen the exhaust, which arises in the combustion in the combustionchambers, is not immediately discharged into the ambient and is insteadfed back into the combustion chambers in order to again be conducted forcombustion.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an internal combustionengine having direct injection wherein further fuel reductions andexhaust gas reductions are possible with the aid of the exhaust-gasfeedback.

This task is solved in a method of the above-mentioned type or for aninternal combustion engine of the above-mentioned type in that thequantity of exhaust gas, which is fed back into the combustion chamber,is differently controlled in both modes of operation with the controlbeing open loop and/or closed loop.

Accordingly, both modes of operation of the internal combustion enginehaving direct injection are considered in the control (open loop/closedloop) of the exhaust gas which is fed back. This means that especiallyin stratified charge operation, the exhaust-gas feedback is controlled(open loop and/or closed loop) differently than in homogeneous operationand the greatest reduction in fuel is achievable in stratified chargeoperation. Thus, in stratified charge operation, it is necessary toreduce the nitrogen oxide emissions which occur in this mode ofoperation via a corresponding exhaust-gas feedback as far as possible.Furthermore, and according to the invention, the transitions which arepresent between the two modes of operation, are controlled differently(open loop and/or closed loop). In total, a system for operating aninternal combustion engine having direct injection is thereby achievedwith which an optimal fuel reduction with simultaneous exhaust gasreduction is obtained based on the particular adapted control (open loopand/or closed loop) in each mode of operation.

In an advantageous configuration of the invention, the quantity offeedback exhaust gas in the first mode of operation is controlled (openloop and/or closed loop) in dependence upon the rpm of the engine and/orupon the torque, which is to be outputted by the engine, and/or the fuelmass which is to be injected into the combustion chamber. Accordingly,in the stratified charge operation, a complex and complete control (openloop and/or closed loop) of the exhaust-gas feedback is carried out. Inthis way, it is achieved that nitrogen oxide emissions, which arise inthe stratified charge operation, are reduced to a minimum with the aidof the exhaust-gas feedback. According to the invention, the reductionsin fuel, which are possible in stratified charge operation, areachievable with a simultaneous reduction in exhaust gas.

It is especially purposeful when the following are considered: theintake air temperature and/or the engine temperature and/or the ambientpressure and/or the degree of tank venting and/or the like. In thecontrol (open loop and/or closed loop) according to the invention of theexhaust-gas feedback in layered charge operation, not only are thedynamic operating conditions considered such as the rpm of the enginebut also the statistical operating conditions such as the enginetemperature. In this way, the control (open loop and/or closed loop) isoptimally adapted to the conditions of the internal combustion engineand an optimal reduction of the generated exhaust gas is therebyachieved.

In an advantageous further improvement of the invention, the quantity ofthe exhaust gas, which is fed back into the combustion chamber, iscontrolled (open loop and/or closed loop) in dependence upon theintake-manifold pressure for a switchover into the first mode ofoperation. In this way, it is achieved that a transition as uniform aspossible is present with the switchover from the homogeneous operationinto the stratified charge operation. In this connection, it isespecially purposeful when the exhaust-gas feedback is adapted to thedynamic of the intake manifold.

In an advantageous embodiment of the invention, a constant quantity andespecially a small quantity or even no exhaust gas is fed back in thesecond mode of operation. In the homogeneous operation, only a small oreven no exhaust-gas feedback is therefore required. In this way, it isavoided in homogeneous operation that a feedback of exhaust gas which istoo high leads to disturbances of the combustions in the combustionchambers.

In an advantageous improvement of the invention, for a switchover intothe second mode of operation, an actual switchover is only made after apregiven time duration. Because of the dynamic of the exhaust-gasfeedback, a larger quantity of exhaust is fed back after a switchoverwhich is to be made. If, under these preconditions, a switchover weremade into the stratified charge operation, this could lead to combustionmisfires or the like. Therefore, the actual switchover into thestratified charge operation is delayed. In this way, combustion misfiresare reliably avoided. During this delay, the exhaust-gas feedback isalready adjusted to the value required for the stratified chargeoperation, that is, to a small quantity or even no feedback exhaust gas.

In an advantageous embodiment of the invention, the quantity of theactual fed back exhaust gas is determined and is compared to the desiredquantity of the fed back exhaust gas and a correction is carried out independence thereon. Thus, a desired/actual comparison is carried out onthe basis of which the exhaust-gas feedback is then influenced. In thisway, a rapid and precise adaptation of the exhaust-gas feedback to thechanges, for example of the operating conditions of the engine, isachieved.

In a further advantageous embodiment of the invention, the exhaust gasis fed back via an internal exhaust-gas feedback and/or via an externalexhaust-gas feedback into the combustion chamber of the engine. For theexternal exhaust-gas feedback, it can be concerned with an exhaust-gaspipe which connects the exhaust-gas end of the engine to the intake endthereof. It is especially purposeful when an exhaust-gas feedback valveis provided in this exhaust-gas pipe which is adjustable for controlling(open loop and/or closed loop) the quantity of the exhaust gas fed back.In this way, it is especially possible in a simple manner to control(open loop and/or closed loop) the exhaust which is fed back via theexternal exhaust-gas return path. An internal exhaust-gas return pathcan, for example, relate to a displacing mechanism for the camshaft withwhich it can be achieved that the inlet and outlet valves, which arecontrolled by the camshaft, are at least opened simultaneously for ashort time. An exhaust-gas feedback via the outlet and inlet valves cantake place during this short time duration.

In an advantageous further improvement of the invention, the quantity ofthe actual fed back exhaust gas is determined in dependence upon: theintake manifold pressure and/or the inducted air mass and/or theexhaust-gas temperature. It is especially purposeful when the positionof the exhaust-gas return valve and/or the position of the camshaft isdetected by the control apparatus. In this way, it is possible torapidly and precisely determine the quantity of the actual fed backexhaust gas and to consider the quantity of the fed back exhaust gas inthe control (open loop and/or closed loop).

In a further advantageous improvement of the invention, the quantity ofthe exhaust gas, which is returned into the combustion chamber of theengine, is considered in the control (open loop and/or closed loop) ofthe fuel mass which is to be injected into the combustion chamber and/orof the ignition spark igniting the fuel in the combustion chamber. Inthis way, it is achieved that the effect of the fed back exhaust gas onthe combustion leads to no change of the combustion process.

The realization of the method of the invention in the form of anelectric storage medium is of special significance. This storage mediumis provided for a control apparatus of an internal combustion engine andespecially of a motor vehicle. A program is stored on the electricstorage medium which can be run on a computer apparatus (especially on amicroprocessor) and is suitable for carrying out the method of theinvention. In this case, the invention is realized by a program storedon the electric storage medium so that this storage medium, which isprovided with the program, defines the invention in the same manner asthe method for which the execution of the program is suitable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block circuit diagram of an embodiment of acontrol of the exhaust-gas feedback according to the invention;

FIG. 2 shows a schematic block circuit diagram of a desired valuegeneration for the control of FIG. 1; and, FIG. 3 shows a schematicblock circuit diagram of a further consideration of the desired valuegeneration of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, a control 1 is shown for the exhaust-gas feedback for aninternal combustion engine having direct injection. In this control, adesired value generation 2 is provided which makes available a desiredvalue magrdes for the quantity of the exhaust gas to be fed back. Thisdesired value generation 2 is explained in greater detail with respectto FIG. 2.

Corresponding to FIG. 1, the desired value magrdes is supplied to acomparator 3 and a drive unit 4. In the comparator 3, the desired valuemagrdes is compared to an actual value magract of the quantity of theexhaust gas to be fed back and a corrective value dmagr is generated independence upon the difference and is likewise supplied to the driveunit 4.

The exhaust-gas feedback is influenced with the aid of the drive unit 4.Thus, it is possible that the drive unit 4 influences an externalexhaust-gas feedback in that an exhaust-gas feedback valve 5 is adjustedby the control unit 4. In this way, so much more exhaust gas is fed backinto the combustion chambers of the engine the more the exhaust-gasreturn valve is opened. Furthermore, it is possible that the drive unit4 influences an internal exhaust-gas feedback in that the camshaft 6 ofthe engine is shifted by the drive unit. Then, the exhaust gas is fedback into the combustion chambers for that time duration during whichthe inlet and outlet valves are simultaneously opened by the camshaft.

The exhaust-gas feedback valve 5 and the camshaft 6 are influenced bythe drive unit 4 in dependence upon the desired value magrdes and thecorrective value dmagr. The desired value magrdes is thereforecontinuously corrected by the corrective value dmagr. The division ofthe total exhaust-gas feedback to the external and the internalexhaust-gas feedback can take place with respect to characteristicfields or other relationships.

The position of the exhaust-gas feedback valve 5 and the position of thecamshaft 6 can be detected with the aid of sensors. These signals aresupplied to an actual value generator 7 which determines the actualvalue magract for the actual quantity of the fed back exhaust gas basedon this signal as well as additional data such as the intake manifoldpressure and/or the inducted air mass and/or the exhaust-gastemperature. The actual value magract is then supplied to the comparator3 as already mentioned.

With the aid of the control 1, which is shown in FIG. 1, the quantity ofthe exhaust gas, which is fed back into the combustion chambers of theengine, is controlled to the desired value magrdes. The desired valuemagrdes is pregiven by the desired-value generator 2 and is thereaftercompared to the actual value magract and is then correspondinglycorrected. The adjustment of the exhaust-gas feedback takes place withthe aid of the drive unit 4 and the adjustment of the exhaust-gasfeedback valve 5 and/or the camshaft 6.

The desired-value generator 2 of FIG. 1 is shown in greater detail inFIG. 2. There, a first value egr1 for a desired exhaust-gas quantity tobe fed back is determined from the rpm of the engine nmot and theindicated torque Mi or the fuel mass mk, which is to be injected, via acharacteristic field 8. This value relates to a theoretical orstandardized operating state of the engine, that is, to a specifictemperature of the engine for example. From this first value egr1, asecond value egr2 is determined for the desired exhaust-gas quantity tobe fed back in a block 9 while considering the actual operating state ofthe engine. For example, in the block 9, the following are, for example,considered: the inducted air temperature tans and/or the enginetemperature tmot and/or the ambient temperature pu and/or the degree oftank venting and/or other data as to the actual operating state of theengine.

The second value egr2 is thereafter distributed with the aid of switch10. Switch 10 can assume four switching positions which can be selectedwith the aid of four binary signals.

If there is a signal B_sh=1, then this means that there should be aswitchover from stratified charge operation into the homogeneousoperation. In this case, the second value egr2 is connected to theterminal “stratified→homogeneous”. If the signal is B_hs=1, then thismeans that there should be a switchover from homogeneous operation intothe stratified charge operation. In this case, the second value egr2 isconnected to a terminal “homogeneous→stratified”. If the signal isB_sa=1 or the signal is a signal B_st=1, then this means that the engineis in a starting operation or is in overrun operation. In this case, thesecond value egr2 is connected to a terminal “start, overrun”. In allother cases, the second value egr2 is connected to a terminal “other”.

Should there be a switchover from the stratified operation into thehomogeneous operation, that is B_sh=1, then the second value egr2 isapplied to a time-delay element 11 and a block 12. The desired valuemagrdes is formed for the quantity of the exhaust gas to be fed back bythe block 12 which is constant in homogeneous operation. This appliesalso to magrdes=c wherein c is a smaller value or can even be zero. Thevalue c can but need not be dependent from the second value egr2. Thisconstant value c for the desired value magrdes is made immediatelyavailable. The time duration TAGRDYN of the time-delay element 11 isdependent upon the dynamic of the exhaust-gas feedback and the dynamicof the intake manifold of the engine. Only after the time durationTAGRDYN has elapsed, is a binary signal B_egrsh generated by thetime-delay element 11 after which there is an actual switchover intohomogeneous operation.

Because of the time duration TAGRDYN, it is achieved that the exhaustgas, which is present in the exhaust-gas feedback and in the intakemanifold, is still combusted during stratified charge operation and onlythen is there a switchover into the homogeneous operation with itslesser demand of exhaust gas to be fed back. Insofar, combustionmisfires are therefore avoided which are caused by an excess of fed backexhaust gas.

If there is to be a switchover from homogeneous operation into thestratified charge operation (that is, B_sh=1), then the second valueegr2 is applied to a block 13 with which the second value egr2 isadapted to the dynamic of the intake manifold of the engine. The desiredvalue magrdes is therefore generated from the second value egr2 by acorresponding function. With this function, there can be, for example, atime-dependent adaptation so that the desired value magrdes correspondsessentially to the second value egr2 for the desired exhaust-gasquantity to be fed back at least in the steadystate condition.Accordingly, in stratified charge operation, the quantity of the exhaustgas, which is to be fed back is controlled to this desired value magrdeswith the aid of the control 1 of FIG. 1. In this stratified operation, aquantity of exhaust gas, which is essentially different from zero, isfed back into the combustion chambers of the engine.

If the engine is in a starting operation or in overrun operation, thenthe desired value magrdes is adjusted with the aid of block 14 to aconstant value d. Here, the concern can be a small quantity or even nofed back exhaust gas. In all other cases, the desired value magrdescorresponds directly to the second value egr2.

The combustion in these combustion chambers is influenced by theexhaust-gas quantity fed back into the combustion chambers of theengine. This is again compensated by corresponding corrections of thequantities which otherwise characterize the combustion. One suchcompensation is, for example, necessary in stratified charge operationbecause there, the most exhaust gas is fed back and this fed backexhaust gas therefore operates the most on the combustion.

FIG. 3 shows how the desired value magrdes, which is generated by thedesired-value generation 2, operates on other quantities which influencethe combustion. Accordingly, the following are influenced in dependenceupon the desired value magrdes especially via corresponding functionsand/or characteristic fields 15, 16, 17, 18 and 19: the ignition anglezwegrs and/or the injection start asbegrs and/or the injection endaseegrs for the fuel to be injected and/or the fuel injection pressurepregrs and/or the intake manifold pressure psegrs and/or the injectionquantity mkegrs. This influencing can furthermore be dependent also uponthe rpm nmot of the engine.

The exhaust-gas quantity, which is fed back into the combustion chambersof the engine during stratified charge operation and during homogeneousoperation, is controlled (open loop and/or closed loop) by a controlapparatus especially with respect to a low fuel consumption and/or areduced exhaust-gas development. Especially the exhaust-gas feedback iscontrolled (open loop and/or closed loop) with a view to the leastpossible nitrogen oxide emissions. For this purpose, the controlapparatus is provided with a microprocessor which has a program storedin a storage medium and especially in a read-only-memory. This programis suitable to execute the above-mentioned control (open loop and/orclosed loop). The control apparatus is especially suited to execute theblock diagrams shown in FIGS. 1 to 3 in the form of a sequence. For thispurpose, input signals such as nmot, tans and the like are applied tothe control apparatus. These input signals indicate operating states ofthe engine measured via sensors and the control apparatus generatesoutput signals such as the adjustment signals for the exhaust-gasfeedback valve 5 and/or the camshaft 6 with which the performance of theengine can be influenced via actuators in correspondence to the desiredcontrol (open loop and/or closed loop).

What is claimed is:
 1. A method of operating an internal combustionengine including an internal combustion engine of a motor vehiclewherein the fuel is injected directly into the combustion chamber of theengine either in a first operating mode during a compression phase or ina second operating mode during an induction phase, the method comprisingthe steps of: feeding back at least a portion of the exhaust gasgenerated during combustion into the combustion chamber; controlling thequantity of the exhaust gas fed back into the combustion chamberdifferently in the two modes of operation; and, utilizing the quantityof the exhaust gas, which is fed back into the combustion chamber of theengine, in the control of at least one of the fuel mass, which isinfected into the combustion chamber, and the ignition spark, whichignites the fuel in the combustion chamber; and, the control of saidexhaust gas being at least one of an open-loop control and a closed-loopcontrol.
 2. The method of claim 1, wherein: in the first mode ofoperation, the quantity of the exhaust gas, which is fed back into thecombustion chamber, is controlled in dependence upon at least one of thefollowing: the rpm (nmot) of the engine; the torque Mi, which is to beoutputted by the engine; and, the fuel mass (mk) which is to be injectedinto the combustion chamber.
 3. The method of claim 1, wherein: at leastone of the following is considered: the inducted air temperature (tans);the engine temperature (tmot); the ambient pressure (pu); and, thedegree of tank venting.
 4. The method of claim 1, wherein: the quantityof the exhaust gas, which is fed back into the combustion chamber, iscontrolled in dependence upon the intake manifold pressure when there isa switchover into the first mode of operation.
 5. The method of claim 1,wherein: a constant quantity (c), especially a small quantity or even noexhaust gas, is fed back in the second mode of operation.
 6. The methodof claim 1, wherein: for a switchover into the second mode of operation,an actual switchover is made only after a pregiven time duration(TAGRDYN).
 7. The method of claim 1, wherein: for at least one of startand overrun operation of the engine, a constant quantity (d), especiallya small quantity or even no exhaust gas, is fed back.
 8. The method ofclaim 1, wherein: the exhaust gas is fed back into the combustionchamber of the engine via at least one of the following: an externalexhaust-gas feedback and an internal exhaust-gas feedback.
 9. The methodof claim 1, wherein: the quantity of the actually fed back exhaust gasis determined in dependence upon at least one of the intake manifoldpressure, the inducted air mass and the exhaust-gas temperature.
 10. Amethod of operating an internal combustion engine including an internalcombustion engine of a motor vehicle wherein the fuel is injecteddirectly into the combustion chamber of the engine either in a firstoperating mode during a compression phase or in a second operating modeduring an induction phase, the method comprising the steps of: feedingback at least a portion of the exhaust gas generated during combustioninto the combustion chamber; controlling the quantity of the exhaust gasfed back into the combustion chamber differently in the two modes ofoperation; utilizing the quantity of the exhaust gas, which is fed backinto the combustion chamber of the engine, in the control of at leastone of the fuel mass, which is injected into the combustion chamber, andthe ignition spark, which ignites the fuel in the combustion chamber;and, the control of said exhaust gas being at least one of an open-loopcontrol and a closed-loop control; and, determining the quantity of theactually fed back exhaust gas and comparing said quantity of theactually fed back exhaust gas to the desired quantity of the fed backexhaust gas and executing a correction in dependence thereon. 11.Electric storage medium for a control apparatus of an internalcombustion engine including an internal combustion engine of a motorvehicle and wherein fuel is infected directly into the combustionchamber of the engine either in a first operating mode during acompression phase or in a second operating mode during an inductionphase, the electric storage medium comprising: a program stored thereonsuitable to be run and to execute the following method steps on acomputer apparatus: feeding back at least a portion of the exhaust gasgenerated during combustion into the combustion chamber; controlling thequantity of the exhaust gas fed back into the combustion chamberdifferently in the two modes of operation; and, utilizing the quantityof the exhaust gas, which is fed back into the combustion chamber of theengine, in the control of at least one of the fuel mass, which isinjected into the combustion chamber, and the ignition spark, whichignites the fuel in the combustion chamber; and, the control of saidexhaust gas being at least one of an open-loop control and a closed-loopcontrol.
 12. An internal combustion engine including an internalcombustion engine for a motor vehicle, the engine comprising: aninjection valve with which fuel can be injected into a combustionchamber either in a first mode of operation during an induction phase orin a second mode of operation in an compression phase; means for feedingback the exhaust gas into the combustion chamber; a control apparatusfor controlling the quantity of the exhaust gas, which is fed back intothe combustion chamber, differently in the two modes of operation; and,wherein the control of said exhaust gas is at least one of an open-loopcontrol and a closed-loop control; and, means for utilizing the quantityof the exhaust gas, which is fed back into the combustion chamber of theengine, in the control of at least one of the fuel mass, which isinfected into the combustion chamber, and the ignition spark, whichignites the fuel in the combustion chamber; and, the control of saidexhaust gas being at least one of an open-loop control and a closed-loopcontrol.
 13. The internal combustion engine of claim 12, wherein: anexhaust-gas feedback valve is provided which can be adjusted by thecontrol apparatus to control the quantity of fedback exhaust gas. 14.The internal combustion engine of claim 12, wherein: a camshaft isprovided which opens at least one of an inlet valve and an outlet valveand is adjustable by the control apparatus for controlling the quantityof fedback exhaust gas.
 15. The internal combustion engine of claim 14,wherein: at least one of the position of the exhaust-gas feedback valveand the position of the camshaft can be detected by the controlapparatus.